The invention concerns a method for detecting irregularities in a product, in which at least one light band, more specifically consisting of one or more laser beams, is directed towards this product, which moves in a particular direction through a detection zone, so that said light band, which preferably moves transversely across the path of the product, is at least partially scattered and/or reflected by said product, and the scattered light is at least partially detected by at least one detector, the light stream of the scattered light then being compared with the light stream of the scattered light from a good part of the product that shows no irregularities in order to detect irregularities in the product.
By xe2x80x9cscattered lightxe2x80x9d is meant in this description on the one hand the light which is diffusely reflected at the surface of a product, and on the other hand the light that is emitted by the product as a result of said light band at least partly penetrating it, spreading into it, and thereby making the corresponding part of the product light up.
According to the state of the art, the light stream of scattered light which is thus detected by at least one detector, is dependent on the position of said band. This means that the value of the signal generated by means of the detector, which determines whether a part of the product must be characterised as a good part or as a foreign component or a part of lower-value, is dependent on the position of the light band.
In order to avoid such dependency, the signal coming from said detector is electronically modified, for example by multiplying it by a factor which is dependent on the position of the light band, so that a signal is obtained which does not depend on the position of the light band.
These modifications require a relatively complex electronic system that considerably increases the cost price of such a method. Moreover, where a product consists of parts that are loose from one another, such corrections generally do not provide any uniform accuracy depending on the position of the light band, for the purposes of detecting irregularities in the product and characterising the latter.
The aim of the invention is to deal with this by proposing a method which does not have these disadvantages, and which ensures that irregularities in a product are detected with uniform sensitivity, and which makes it possible to carry out very good detection or classification, both qualitative and quantitative, in a very economical manner.
To this end, the light stream falling on said detector from the light scattered by part of the product is adjusted in such a manner that it is independent of the position of said part in said detection zone.
The invention also concerns a device for detecting irregularities in a product moving in a particular direction through a detection zone, with at least one detector and means to generate at least one light band directed towards said product and preferably moving perpendicular to the direction of travel of said product, in such a manner that the light from said light band is scattered and/or reflected by part of said product, where said detector is arranged so that this scattered light at least partly falls on it.
This device is characterised by the fact that between said detector and the place where the product moves through the detection zone, an adjusting element is placed that lets through only some of the light scattered by a part the product, in such a manner that the light stream of the scattered light falling on said detector is independent of the position of said part.
Said adjusting element can advantageously comprise a diaphragm with at least one calibrated opening.
In a particular embodiment of the device according to the invention, said diagram has means to adjust the size of said opening.
Said diaphragm can advantageously be provided with small, movable plates at the edge of said opening, where said plates enable the size and/or shape of the opening to be adjusted, in such a manner that the light stream falling on said detector is independent of the position of said light band.
The invention further concerns a sorting apparatus for separating foreign components or lower-value parts from good parts of a product which consists of parts that are loose from each other, where said sorting apparatus is provided with said device. For example, when the product consists of peas, the sorting apparatus makes it possible for lower-value peas such as overripe peas, and foreign objects such as small stones, stalks and suchlike, to be separated from peas that are suitable for human consumption.
Other features and advantages of the invention will be apparent from the following description of several particular embodiments of the method, the device and the sorting apparatus according to the invention; this description is given by way of example only and in no way limits the scope of the protection claimed; the reference numbers below refer to the attached drawings.